This invention relates to the ability to register a pre-printed web to an image currently being printed.
The present invention is primarily aimed at CI (Central Impression) Flexographic printing presses. Although the invention is not limited to such a machine or printing method.
CI Flexographic printing is a printing method commonly used on flexible packaging materials. Presently there is a need in the flexible packaging industry to have high quality print on one side of a web with limited printing on the backside. The backside printing is typically one or two colors for trademarks, register marks, or coupons. Trademarks, register marks, and coupons are not, of course, limitations of this invention but rather specific applications for the invention.
In all present methods of reprinting preprinted webs, the web (material) is either printed in one pass through one machine or requires an extensive amount of downstream equipment added to the printing press. On a CI Flexographic printing press, back side printing (printing on the reverse side of the web) can only be achieved by running a pre-printed web through the press after reversing the web or by adding extra print stations in-line with the CI printing section.
Printing in register to a pre-printed web on a CI Flexographic press is presently achieved by adding equipment between the unwind station and the CI (printing) section of the machine. The additional equipment is typically a web compensating unit, a register controller, and a driven draw roll. This equipment varies the web path distance between the driven draw roll and the print section to adjust register between the preprinted image and the new image.
Another present method is the so-called double-pass press. On this CI printing machine, the web width is less than half the width of the printing press. The material is delivered from the unwind and printed with the material aligned to one side of the press. This is the first pass. After going through the dryer section, the material is turned over and run on the other side of the machine (parallel to the first pass). This is the second pass. The material again goes through the dryer and to the rewind.
In-line printing with a CI printing press requires an additional print section, a compensating unit (web or cylinder), a register controller, and driven draw roll. Depending on the machine configuration, a web turning bar assembly is also needed to allow backside printing.
The limitation of the present art is the ability to print limited colors or images on the backside of the full web width of flexible packaging which is typically printed using the CI flexographic process. A CI press physically can not print on the reverse side without running the web for a second pass. This requires the use of additional drive systems, register systems, web compensation units and, typically, additional print stations. Space and cost limitations hamper the application of these technologies.
The present art also has a limited ability to run both extensible and non-extensible web materials.
U.S. Pat. No. 3,949,949 relates to controlling tension of a paperboard container to position a pre-printed stock with a punch press. This patent has the limitation of controlling the rate of feed as opposed to the position of the material. This patent is also limited in scope to non-extensible materials.
U.S. Pat. No. 5,485,386 relates to controlling elongation of a web during a single pass printing process. The system controls repeat length. It is limited by not controlling register during a second pass print run.
U.S. Pat. No. 5,709,331 relates to controlling elongation (repeat length) of a printed material. This method is limited in that it cannot control register of a pre-printed web. The system does not monitor register marks and compare them to press position.
U.S. Pat. No. 5,813,587 relates to registering creases while laminating paperboard. The patent does not allow for registering pre-printed webs. It also does not relate to controlling tension based upon the position of register marks with respect to a print (or other) operation. The patent is also limited to non-extensible materials.